The present invention concerns glues based on cyanacrylic acid esters with a shortened setting time and their use on porous surfaces.
It is known that glues based on cyanacrylic acid esters are characterized by short setting times during the bonding or cementing of various materials. This hardening is generally due to an anionically released polymerization. While metal surfaces, glass etc. can be bonded very rapidly with each other, difficulties are encountered in the bonding of porous surfaces with these glues. Such difficulties are particularly observed in materials, like wood, paper, leather, etc.
In an .alpha.-cyanacrylic acid ester is used to bond materials whose surfaces show an acid reaction, the anionic polymerization is inhibited, and the setting time is extended. The adhesive strength is not satisfactory either. Wood has generally a moisture content of about 10% by weight under normal conditions (22.degree. C. at a relative humidity of 40%). Despite this high water content of the woody tissue and on the surface of the wood materials, a setting time or more than 10 to 20 minutes is required to bond with the known cyanacrylic acid ester based glues. Since the cyanacrylic acid esters penetrate during this time into the woody tissue, it is difficult to bond wood with these cements. Accordingly the effectiveness of these glues as quick setting cements drops drastically.
It is known that these difficulties can be at least partly eliminated by the addition of macrocyclic polyethers, also called crown ethers. When these compounds or certain nonionic tensides based on polyethylene glycols are added, the hardening time of the cyanacrylic acid esters is considerably reduced.
However, the addition of these known compounds can also lead to an undesired destabilization of the cyanacrylic acid esters, so that they have only a limited storage time, which is naturally undesired.